Method of filling a tube system with a rinsing liquid and a tube system for use with this method

ABSTRACT

A tube system comprising a blood inlet line with an arterial patient connection and a blood return line with a venous patient connection, where a rinsing liquid inlet line branches off from the blood inlet line downstream from the arterial patient connection, and a rinsing liquid return line branches off from the blood return line upstream from the venous patient connection is filled while maintaining sterility in that rinsing liquid is pumped from a rinsing liquid container through the rinsing liquid inlet line, the blood inlet line, the blood return line and the rinsing liquid return line, establishing a liquid connection between the rinsing liquid inlet line and return line. The venous patient connection is sealed liquid-tight with a venous safety cap, and the arterial patient connection is sealed liquid-tight with an arterial safety cap. The safety caps are removed from the patient connections for connecting the tube system to the patient.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of filling a tubesystem with a rinsing liquid while maintaining sterility, and a tubesystem for use with this method. In addition, the present inventionrelates to a safety cap unit for use with the tube system.

BACKGROUND INFORMATION

[0002] When treating various acute and chronic diseases, it may benecessary to perform a treatment of body fluids in an extracorporealcirculation outside the body. Such treatments are performed inhemodialysis or hemofiltration, where blood is subjected to a dialysistreatment in a dialyzer. In addition to hemodialysis or hemofiltrationequipment, cell separators are also known which make it possible toseparate blood of a patient into fractions. Cell separation is alsoperformed in an extracorporeal circulation.

[0003] Since the blood treatment must be performed under sterileconditions, tube systems which are intended for a single use typicallyare used with current blood treatment or processing equipment. Forconnection to the patient, the single-use tube systems have a bloodinlet line with an arterial patient connection and a blood return linewith a venous patient connection.

[0004] To prepare an extracorporeal circulation, the part of the tubesystem intended for blood typically is rinsed with a physiologicalsaline solution and is filled so as to admit as little air as possibleby using either a non-recirculating or recirculating method of filling.

[0005] With non-recirculating methods of filling the tube system, thesaline solution is drawn from a container through the blood inlet line,and then the rinsing liquid flows through the tube system and is sentthrough the blood return line into another container which serves tohold the used saline solution. This method has the disadvantage of arelatively high consumption of rinsing liquid.

[0006] Recirculating methods, where the supply container and thecollecting container are combined, differ from the non-recirculatingmethods of filling the tube system. In this way, the saline solution cancirculate through the tube system repeatedly without having to refillthe container. For connecting the patient connections, the container hasconnection parts with self-sealing septa which are punctured by thecannulas of the patient connections. The advantage of the recirculatingmethods is the low consumption of rinsing liquid. However, they have thedisadvantage that when connecting the patient connections to thecontainer, there is the risk that the cannulas of the patientconnections might be damaged. Optimally, these cannulas should be groundand sharp for puncturing the containers of the patient. European PatentApplication No. 203,513 A, for example, discloses a medical bagarrangement for recirculation of the rinsing liquid.

[0007] European Patent Application No. 305,364 A describes a method offilling a tube system where the patient connections are short-circuitedby a bridge, with the saline solution being supplied through a sidebranch of the tube system. The patient connections can be introducedinto the short-circuit piece at the factory, so that the tube system isavailable to the user in a sterile condition. One disadvantage is thatthe rinsing liquid recirculates through the patient connections. Thisleads to a high flow resistance, especially with so-called closedsystems in which the needle adapters are fixedly attached to thecannulas. Since the two patient connections are interconnected by theshort-circuit piece, there is the risk, especially with complicated tubesystems such as those conventionally used in cell separation, that oneof the patient connections might become detached from the short-circuitpiece when inserting the tube system, thus violating the sterilityrequirement. Another disadvantage is that one patient connection isalready being exposed to an unsterile environment when the otherconnection is being removed from the short-circuit piece. Therefore, thetube connection must be connected to the patient very quickly.

[0008] There are also extracorporeal tube systems with regionalanticoagulation. This is understood to include systems in which blood istreated with anticoagulant not inside the patient but instead onlywithin the extracorporeal circulation. This is usually accomplished witha sodium citrate solution which is added to the blood downstream fromthe patient connection on the suction side. Such systems generally havea so-called “keep vein open” function which makes it possible to rinsethe coagulable blood out of the cannulas and back into the patient inthe event of a machine shutdown, thereby preventing coagulation insidethe cannulas. Tube systems having a keep vein open function typicallyhave rinsing liquid lines which open into the blood inlet and returnlines in the immediate vicinity of the patient connections. In the caseof a machine shutdown, the saline solution is supplied from a bag to thetube system through the rinsing liquid lines.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a method thatpermits filling of a tube system, even those with regionalanticoagulation, while maintaining sterility without increasing the flowresistance or exposing one of the patient connections to an unsterileenvironment when the other connection is ready for connection to thepatient.

[0010] The present invention provides a method of filling a tube systemwith a rinsing liquid while maintaining the sterility of the tubesystem, comprising a blood inlet line with an arterial patientconnection and a blood return line with a venous patient connection,where a rinsing liquid inlet line branches off from the blood inlet linedownstream from the arterial patient connection, and a rinsing liquidreturn line branches off from the blood return line upstream from thevenous patient connection. The method is characterized in that rinsingliquid is conveyed from a rinsing liquid container back into the rinsingliquid inlet line, establishing a liquid connection between the rinsingliquid inlet and return lines, with the venous patient connection beingsealed liquid-tight with a venous safety cap and the arterial patientconnection being sealed liquid-tight with an arterial safety cap whichcan be removed from the patient connections in order to connect the tubesystem.

[0011] The present invention also provides a tube system for use withthe present method, with a blood inlet line (5) having an arterialpatient connection (1) which is sealed liquid-tight with an arterialsafety cap (2) which can be removed from the patient connection forconnecting the tube system. A blood return line (15) has a venouspatient connection (3) which is sealed liquid-tight with a venous safetycap (4) that can be removed from the patient connection for connectingthe tube system. A rinsing liquid inlet line (21) branches off from theblood inlet line downstream from the arterial patient connection, and arinsing liquid return line (25) branches off from the blood return lineupstream from the venous patient connection, with the rinsing liquidinlet line and the rinsing liquid return line being connected to arinsing liquid container (20) that accommodates the rinsing liquid. Afirst cut-off device (30) is connected to the rinsing liquid inlet linedownstream from the rinsing liquid container, and a second cut-offdevice (32) is connected to the rinsing liquid return line upstream fromthe rinsing liquid container. The tube system is characterized in that ashort-circuit line (35) connecting the rinsing liquid inlet line (21)and rinsing liquid return line (25) is provided, with a third cut-offdevice (36) or a pressure control valve (51) being connected to thisline.

[0012] The present invention further provides a safety cap unit for atube system for use with the present method with an interior venous andarterial chamber (42, 43) for accommodating the venous and arterialpatient connections (1, 3) of the tube system under sterile conditions,and with the interior venous chamber (43) being connected to theenvironment by a hydrophobic membrane (47).

[0013] With the method according to the present invention, the rinsingliquid is recirculated not through the patient connections but throughthe rinsing liquid lines. The rinsing liquid flows from a rinsing liquidcontainer through the rinsing liquid inlet line, the blood inlet line,the blood return line and the rinsing liquid return line and then goesback to the rinsing liquid inlet line. Even if the safety cap becomesdetached from one of the patient connections, the other patientconnection is still exposed to a sterile environment.

[0014] This method can be implemented in many variants and combinationswhich are made possible by different tube systems. The main points ofthe modifications are the safety caps on the patient connections and theline configuration of the tube system in the vicinity of the rinsingliquid containers.

[0015] The term “patient connection” is understood below to refer to allmeans making it possible to connect the tube system to the blood vesselsof the patient. The patient connections may be designed as needleadapters for attaching cannulas, but the cannulas may also be alreadyattached to the needle adapters or they may be designed in one piecewith the connections. Safety caps are hereinafter understood to refer toall devices enclosing the patient connection under sterile conditions.

[0016] In order for the safety caps to be filled completely with rinsingliquid during the rinsing operation, air in the line section of theblood inlet or return line upstream or downstream from the branch in therinsing liquid inlet or return line is preferably let out of the safetycaps. For this purpose, the safety caps have hydrophobic membranes thatprevent the passage of liquid but allow air to escape.

[0017] The venous and arterial safety caps may be designed as separateparts, but it is also possible for the two safety caps to form one unit.If the venous and arterial safety caps are designed in one piece, theinterior chambers of the safety caps can be vented independently of oneanother, but it is also possible for the air in the venous safety cap tobe transferred to the arterial safety cap.

[0018] The safety cap unit for a tube system for use with the onevariant of the method according to the present invention has an interiorvenous chamber and an interior arterial chamber to accommodate thesterile venous and arterial patient connections, respectively, where atleast the interior venous chamber is connected to the environmentthrough a hydrophobic membrane, while the safety cap unit for a tubesystem for use with the other variant of the method according to thepresent invention has two interior chambers connected to one another bya hydrophobic membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The method according to the present invention and severalembodiments of the tube system for use with the method according to thepresent invention are explained below with reference to the figures, inwhich:

[0020]FIG. 1 shows a schematic diagram of one embodiment of a tubesystem for a cell separator together with the essential components ofsame;

[0021]FIG. 2 shows a schematic diagram of a first embodiment of thesafety caps of the tube system from FIG. 1 which close the patientconnections;

[0022]FIG. 3 shows a schematic diagram of another embodiment of the lineconfiguration to establish a liquid connection between the rinsingliquid inlet and return lines of the tube system from FIG. 1;

[0023]FIG. 4 shows a schematic diagram of another embodiment of the lineconfiguration to establish the flow connection between the rinsingliquid inlet and return lines of the tube system from FIG. 1;

[0024]FIG. 5 shows a schematic diagram of another embodiment of the lineconfiguration to establish the liquid connection between the rinsingliquid inlet and return lines of the tube system from FIG. 1;

[0025]FIG. 6 shows a schematic diagram of another embodiment of thesafety caps closing the patient connections with a liquid-tight seal forthe tube system from FIG. 1;

[0026]FIG. 7 shows a schematic diagram of a safety cap unit foraccommodating the patient connections for the tube system from FIG. 1;

[0027]FIG. 8 shows another embodiment of the line configuration forestablishing the flow connection between the rinsing liquid inlet andreturn lines; and

[0028]FIG. 9 shows a schematic diagram of another embodiment of thesafety cap unit for accommodating the patient connections.

DETAILED DESCRIPTION

[0029]FIG. 1 shows one embodiment of a tube system, referred to as aplatelet set, together with components of a cell separator into whichthe tube system intended for a single use can be inserted.

[0030] The tube system has an arterial patient connection 1, which has aliquid-tight seal provided by an arterial safety cap 2, and a venouspatient connection 3, which has a liquid-tight seal provided by a venoussafety cap 4. A blood inlet line 5 is connected to the arterial patientconnection 1 and to the blood inlet of a separation chamber 6. A wholeblood pump 7 which pumps the blood of the patient into the separationchamber 6 is provided in the blood inlet line 5. The whole blood isseparated into several fractions in separation chamber 6. Plasmadepleted of platelets is removed from the separation chamber 6 through aplasma line 8 that is connected to the separation chamber 6 and isprovided with a plasma pump 9. Plasma line 8 leads to the inlet of anair detector 10. The platelet fraction is removed from the separationchamber through a platelet line 11, which is connected to separationchamber 6 and to a cell pump 12, and is sent to a transfer bag 13. Theerythrocyte fraction is removed through an erythrocyte line 14 connectedto the separation chamber. The erythrocyte line 14 also leads to theinlet of air detector 10. The outlet of air detector 10 is connected tothe venous patient connection 3 by a blood return line 15.

[0031] The tube system also has an anticoagulate, for example ACD (acidcitrate dextrose), line 16 opening into blood inlet line 5 at a branch24 near the arterial patient connection 1. At its other end, ACD line 16has a connector 16 a for connection to an ACD bag 18. A drip chamber 19is connected to the ACD line.

[0032] The tube set also has two rinsing liquid lines opening into theblood inlet or return line near the venous and arterial patientconnection, respectively. With previous tube systems, these lines servedto supply rinsing liquid, in particular a saline solution from a rinsingliquid bag 20 in the case of a standstill, to rinse coagulable bloodfrom the connections back to the patient. With the method according tothe present invention, however, these lines serve to fill the tubesystem.

[0033] The rinsing liquid inlet line 21, having a connector 22 forconnection to an outlet 23 of the bag 20, opens into blood inlet line 5through branch 17 on a branch 24 near the arterial patient connection 1,while rinsing liquid return line 25, which has a connector 26 to theconnection at an inlet 27 of the bag 20, branches off from blood returnline 15 at a branch 28 near the venous patient connection 3. A firstdrip chamber 29 is connected to the rinsing liquid inlet downstream fromthe connector 22, and a first roller clamp 30 is connected downstreamfrom this drip chamber. A second drip chamber 31 is connected to therinsing liquid return line upstream from connector 26, and a secondroller clamp 32 is connected upstream from this drip chamber.

[0034] The tube system may also include other components and is notlimited to the components shown.

[0035]FIG. 2 shows the tube ends of blood inlet line 5 and blood returnline 15 together with patient connections 1, 3 which are sealedliquid-tight with safety caps 2, 4. The two patient connections 1, 3each have a needle adapter 1 a, 3 a to which are attached cannulas 1 b,3 b. Cylindrical safety caps 2, 4 sitting on the connection pieces 1, 3are sealed with ring gaskets 1 c, 3 c with respect to needle adapters 1a, 3 a under sterile connections. Venous safety cap 4 has an air outletorifice 4 b which is sealed with a hydrophobic membrane 4 a, i.e., amembrane that is permeable for air but not for liquid, whereas thearterial safety cap 2 seals the arterial patient connection so it isboth airtight and liquid-tight.

[0036] The tube system described with reference to FIGS. 1 and 2 issupplied as a sterile unit with the safety caps attached to the patientconnections and the tube system is filled as described below.

[0037] The tube system is inserted into the cell separator with safetycaps 2, 4 attached to patient connections 1, 3. With roller clamps 30,32 closed, connectors 22, 26 of the rinsing liquid inlet and returnlines 21, 25 are connected to the outlet and inlet 23, 27, respectively,of the rinsing liquid bag 20. Then, with roller clamps 30, 32 opened,operation of whole blood pump 7 is started, pumping rinsing liquid outof the rinsing liquid bag. The rinsing liquid flows through rinsingliquid inlet line 21, branch 24 and blood inlet line 5 into separationchamber 6 and back out of separation chamber 6 and into bag 20 throughblood return line 15 and rinsing liquid return line 25. The rinsingliquid is then recirculated repeatedly in this closed circuit. Air inthe line section of blood return line 15 downstream from branch 28 isreleased through hydrophobic membrane 4 a of venous safety cap 4, whilethis line section and the safety cap are filled completely with rinsingliquid. After the end of the rinsing operation, the arterial and venoussafety caps 2, 4 are removed from patient connections 1, 3, and cannulas1 b, 3 b of the patient connections are punctured to connect to theblood system of the patient.

[0038]FIG. 3 shows the line configuration in the area of rinsing liquidbag 20 in another embodiment of the tube system, where the partscorresponding to those in FIGS. 1 and 2 are labeled with the samereference notations. The embodiment in FIG. 3 differs from theembodiment in FIGS. 1 and 2 only in that the rinsing liquid return lineopens into the rinsing liquid inlet line 21 at a connection point 33between the first drip chamber 29 and the first roller clamp 30. Asecond drip chamber is eliminated with this embodiment. The rinsingliquid recirculates through rinsing liquid inlet line 21, blood inletline 5, blood return line 15 and rinsing liquid return line 25. Sincerinsing liquid does not flow through rinsing liquid bag 20, there is norisk of the rinsing liquid becoming contaminated with particles duringrecirculation. In comparison with the embodiment of FIGS. 1 and 2, theembodiment from FIG. 3 has the advantage that the tube system is readyto use immediately after filling. However, with the embodiment fromFIGS. 1 and 2, a level is first established in drip chamber 31, which isfilled completely with rinsing liquid during the filling operation,displacing the air in the rinsing liquid bag.

[0039]FIG. 4 shows the line configuration in the area of the rinsingliquid bag of another embodiment of the tube system, where thecorresponding parts have again been labeled with the same referencenotations. At a connecting point 61 upstream from the second rollerclamp 32, a short-circuit line 35 branches off from the rinsing liquidreturn line 25, opening into the rinsing liquid inlet line 21 at aconnection point 34 downstream from the first roller clamp 30. A thirdcut-off device 36, e.g., a hose clamp, is provided in the short-circuitline 35. In this embodiment, the rinsing liquid is not recirculatedthrough bag 20 but instead through short-circuit line 35 after openingcut-off device 36.

[0040]FIG. 5 shows an alternative embodiment of the tube system with ashort-circuit line, where the parts which correspond to those in FIG. 4have again been provided with similar reference notations. In thisembodiment, the short-circuit line 35 which branches off from therinsing liquid return line 25 at the connection point 61 upstream fromthe second roller clamp 32 opens into the rinsing liquid inlet line 21at a connecting point 37 between the first drip chamber 29 and the firstroller clamp 30. Otherwise, the line configuration corresponds to thatin FIG. 4. Here again, the rinsing liquid is recirculated again throughthe short-circuit line.

[0041]FIG. 6 shows the venous and arterial safety caps in anotherembodiment of the tube system from FIGS. 1 and 2. However, the safetycaps from FIG. 6 can also be used instead of the safety caps from FIG. 2with the tube systems from FIGS. 3, 4 and 5. Venous safety cap 4 fromFIG. 6 corresponds to that of FIG. 2. Therefore, these safety caps arealso labeled with the same reference notations. However, the arterialsafety cap 38 has an air outlet orifice 38 b which is sealed with ahydrophobic membrane 38 a, with the inside of the hydrophobic membranebeing covered with a hydrophilic membrane 38 c. Cylindrical safety cap38 is sealed with a liquid-tight seal with respect to arterial patientconnection 1 with a ring gasket 38 d.

[0042] The two safety caps from FIG. 6 may also be designed in onepiece. FIG. 7 shows such a safety cap unit together with the venous andarterial patient connections 1, 3 of the tube system. The safety capunit 39 has a cylindrical body 40 which is separated by a middlepartition 41 into an interior arterial chamber 42 for accommodating thearterial patient connection 1 and an interior venous chamber 43 foraccommodating the venous patient connection 3. Cylindrical body 40 issealed liquid tight with respect to patient connections 1, 3 with ringgaskets 44, 45. Interior venous chamber 43 is connected to theenvironment through an air outlet orifice 46 at the side, sealed with ahydrophobic membrane 47, while the interior arterial chamber 42 isconnected to the environment at the side to an air outlet orifice 48which is sealed by a hydrophobic membrane 49 whose inside is coveredwith a hydrophilic membrane 50.

[0043] The safety caps from FIG. 6 and the safety cap unit from FIG. 7have the advantage in comparison with the safety caps from FIG. 2 thatthe line section of the blood inlet line 5 upstream from the branch 24and the arterial safety cap 38 is filled completely with rinsing liquid.Both safety caps may also be covered with a hydrophobic or hydrophilicmembrane.

[0044] The method of filling the tube system with the short-circuit line(FIG. 4 or 5) whose patient connections are sealed liquid-tight with thesafety caps from FIG. 6 or the safety cap unit from FIG. 7 is describedbelow. At the start of the rinsing operation, the rinsing liquid bag 20is arranged at an elevated location. The first roller clamp 30 inrinsing liquid inlet line 21 is opened, while the cut-off device 36 inshort-circuit line 35 and the second roller clamp 32 in the rinsingliquid return line 25 are closed. Under the influence of gravity, therinsing liquid flows through rinsing liquid inlet line 21 into bloodinlet line 5. Air in the line section of the blood inlet line 5 upstreamfrom the branch 24 and in the arterial safety cap 38 or the interiorarterial chamber 42 of the safety cap unit 39 is released from thesafety cap or safety cap unit through hydrophilic membrane 38 c or 50and hydrophobic membrane 38 a or 49. The rinsing liquid completely fillsarterial safety cap 38 or interior arterial chamber 42 of safety capunit 39 until it comes in contact with the hydrophobic membrane.Hydrophilic membrane 38 c or 50 on the inside of the hydrophobicmembrane becomes wetted in the process and thus becomes impermeable toair. Only then is operation of whole blood pump 7 started and cut-offdevice 36 in short-circuit line 35 opened to allow the tube system to befilled by recirculation. Air in the line section of blood return line 15downstream from the branch 28 and in venous safety cap 3 or interiorvenous chamber 43 of safety cap unit 39 is released through hydrophobicmembrane 4 a and/or 47. Since hydrophilic membrane 38 c and/or 50 ofarterial safety cap 38 and/or interior arterial chamber 42 of the safetycap unit 39 have become impermeable to air due to being wetted with therinsing liquid, this prevents the whole blood pump 7 from pumping airinto blood inlet line 5.

[0045]FIG. 8 shows the line configuration in the area of the rinsingliquid bag in another embodiment of a tube system with a short-circuitline which does not require operation of a cut-off device in theshort-circuit line during filling. This embodiment differs from theembodiment according to FIG. 4 in that a pressure control valve 51 isprovided instead of a cut-off device 36 in short-circuit line 35, and ahydrophobic filter 52 is arranged between the pressure control valve andbranching point 61. Otherwise, the line configuration corresponds tothat in FIG. 4. Therefore, the corresponding parts are labeled with thesame reference notations. The pressure control valve and the hydrophobicfilter may also replace the cut-off device 36 from the embodiment inFIG. 5.

[0046] Pressure control valve 51 prevents rinsing liquid from enteringrinsing liquid return line 25 and prevents air from being drawn in fromthis line. The pressure limit of the pressure control valve is designedso that the static height of the rinsing liquid bag 20 is not sufficientto open the valve, but the system pressure of blood pump 7 issufficient. Hydrophobic filter 52 upstream from pressure control valve51 serves to provide separation from the air in rinsing liquid returnline 25. If the pressure limit of pressure control valve 51 is so highthat the air can be separated reliably by a hydrophobic filter providedin the drip chamber and by the hydrophobic membrane in the venous safetycap, so that only the relatively small air volume in rinsing liquidreturn line 25 can reenter rinsing liquid inlet line 21, then there isthe possibility of omitting hydrophobic filter 52 upstream from pressurevalve 51.

[0047] With the embodiments according to FIGS. 6 and 7, hydrophilicmembrane 38 c or 50 can also be omitted. With such an embodiment,however, a cut-off device must be provided between the arterial andvenous patient connection 1 and the branch 24 in blood inlet line 5;this cut-off device is closed before the blood pump is turned on afterfilling the blood inlet line under the influence of gravity and is notreopened until being connected to the patient. This cut-off deviceprevents air from being drawn by blood pump 7 through hydrophobicmembrane 38 a or 49 of the arterial safety cap 38 or interior arterialchamber 42 of safety cap unit 39, so that no air enters the line.

[0048]FIG. 9 shows another embodiment of a safety cap unit 53. Safetycap unit 53 has a cylindrical body 54 which is separated by ahydrophobic membrane 56 into an interior arterial chamber 57 toaccommodate arterial patient connection 1 and an interior venous chamber58 to accommodate the venous patient connection 3. The cylindrical body54 is sealed liquid tight with ring gaskets 59, 60 with respect topatient connections 1, 3.

[0049] In the embodiment according to FIG. 9, interior venous chamber 58of safety cap unit 53 is completely filled with rinsing liquid afterblood pump 7 has been turned on, displacing the air in the chamberthrough hydrophobic membrane 56 and into interior arterial chamber 57.Although hydrophobic membrane 56 allows air to pass into blood inletline 5, rinsing liquid does not flow through the safety cap unit.

What is claimed is:
 1. A method of filling a tube system with a rinsing liquid while maintaining sterility of the tube system, the tube system including a blood inlet line with an arterial patient connection, a blood return line with a venous patient connection, a rinsing liquid inlet line branching off from the blood inlet line downstream from the arterial patient connection, and a rinsing liquid return line branching off from the blood return line upstream from the venous patient connection, the method comprising the steps of: conveying rinsing liquid from a rinsing liquid container into the rinsing liquid inlet line, establishing a liquid connection between the rinsing liquid inlet and the rinsing liquid return line, forming a liquid-tight seal for the venous patient connection with a venous safety cap, and forming a liquid-tight seal for the arterial patient connection with an arterial safety cap, wherein the venous safety cap and the arterial safety cap are removable from the venous and arterial patient connections.
 2. The method according to claim 1 wherein the establishing step includes conveying the rinsing liquid from the rinsing liquid return line through the rinsing liquid container into the rinsing liquid inlet line.
 3. The method according to claim 1 wherein the establishing step includes conveying the rinsing liquid from the rinsing liquid return line into the rinsing liquid inlet line, bypassing the rinsing liquid container.
 4. The method according to claim 1 wherein the conveying step includes pumping the rinsing liquid out of the rinsing liquid container using a blood pump connected to the blood inlet line.
 5. The method according to claim 1 wherein the rinsing liquid return line branches off from the blood return line at a first branch, and air in a line section of the blood return line downstream from the first branch is released from the venous safety cap so that the venous safety cap is filled with the rinsing liquid.
 6. The method according to claim 5 wherein the air being released from the venous safety cap is transferred from the venous safety cap to the arterial safety cap so as to establish an air-permeable but liquid-impermeable connection between the venous and arterial safety caps.
 7. The method according to claim 1 wherein the conveying step includes conveying the rinsing liquid out of the rinsing liquid container and into the blood inlet line through the rinsing liquid inlet line under an influence of gravity, while air in a line section of the blood inlet line upstream from a branch in the rinsing liquid inlet line is released from the arterial safety cap so that the arterial safety cap is filled with the rinsing liquid, and sealing the blood inlet line airtight and pumping the rinsing liquid out of the rinsing liquid container by a blood pump connected to the blood inlet line.
 8. The method according to claim 7 wherein the venous safety cap is filled with rinsing liquid by recirculating the rinsing liquid.
 9. A tube system comprising: a blood inlet line having an arterial patient connection; an arterial safety cap for liquid-tight sealing of the arterial patient connection, the arterial safety cap being removable from the arterial patient connection for connecting the tube system, a blood return line having a venous patient connection; a venous safety cap for liquid-tight sealing of the venous patient connection, the venous safety cap being removable from the venous patient connection for connecting the tube system; a rinsing liquid inlet line branching off from the blood inlet line downstream from the arterial patient connection and a rinsing liquid return line branching off from the blood return line upstream from the venous patient connection, the rinsing liquid inlet line and the rinsing liquid return line being connected to a rinsing liquid container for accommodating rinsing liquid; a first cut-off device being connected to the rinsing liquid inlet line downstream from the rinsing liquid container; a second cut-off device being connected to the rinsing liquid return line upstream from the rinsing liquid container; a short-circuit line connecting the rinsing liquid inlet line and the rinsing liquid return line; and at least one of a third cut-off device and a pressure control valve being connected to the short-circuit line.
 10. The tube system according to claim 9 further comprising a first drip chamber arranged in the rinsing liquid inlet line upstream from the first cut-off device and a second drip chamber arranged in the rinsing liquid return line downstream from the second cut-off device.
 11. The tube system according to claim 10 wherein a first end of the short-circuit line branches off from an inlet line section of the rinsing liquid inlet line between the first drip chamber and the first cut-off device, and a second end of the short-circuit line branches off from a return line section of the rinsing liquid return line upstream of the second cut-off device.
 12. The tube system according to claim 10 wherein a first end of the short-circuit line branches off from an inlet line section of the rinsing liquid inlet line downstream from the first cut-off device, and a second end of the short-circuit line branches off from an inlet line section of the rinsing liquid return line upstream from the second cut-off device.
 13. The tube system according to claim 9 wherein the venous safety cap has an air outlet orifice sealed with a hydrophobic membrane.
 14. The tube system according to claim 9 wherein the arterial safety cap has an air outlet orifice sealed by a hydrophobic membrane, an inside of the hydrophobic membrane being covered with a hydrophilic membrane.
 15. The tube system according to claim 9 wherein the venous and arterial safety caps are designed in one piece having an interior venous chamber and an interior arterial chamber.
 16. The tube system according to claim 9 wherein the venous and arterial safety caps are designed in one piece having an interior venous chamber and an interior arterial chamber, the interior arterial chamber being connected to the interior venous chamber through a hydrophobic membrane.
 17. The tube system according to claim 9 wherein at least one of the venous and arterial patient connections has a cannula for connection to a patient, the cannula being surrounded in a sterile manner.
 18. A tube system comprising: a blood inlet line having an arterial patient connection; an arterial safety cap for liquid-tight sealing of the arterial patient connection, the arterial safety cap being removable for connecting the tube system; a blood return line having a venous patient connection; a venous safety cap for liquid-tight sealing of the venous patient connection, the venous safety cap being removable from the venous patient connection for connecting the tube system; a rinsing liquid inlet line branching off from the blood inlet line downstream from the arterial patient connection and a rinsing liquid return line branching off from the blood return line upstream from the venous patient connection and having a free end, the rinsing liquid inlet line being connected to a rinsing liquid container for accommodating the rinsing liquid; a first cut-off device being connected to the rinsing liquid inlet line downstream from the rinsing liquid container, the rinsing liquid inlet line between the rinsing liquid container and the first cut-off device defining a line section of the rinsing liquid inlet line, the free end of the rinsing liquid return line being connected to the line section; and a second cut-off device connected to the rinsing liquid return line.
 19. The tube system according to claim 18 further comprising a drip chamber arranged in the rinsing liquid inlet line between the rinsing liquid container and the first cut-off device.
 20. The tube system according to claim 18 wherein the venous safety cap has an air outlet orifice sealed with a hydrophobic membrane.
 21. The tube system according to claim 18 wherein the arterial safety cap has an air outlet orifice sealed by a hydrophobic membrane, an inside of the hydrophobic membrane being covered with a hydrophilic membrane.
 22. The tube system according to claim 18 wherein the venous and arterial safety caps are arranged in one piece having an interior venous and arterial chamber.
 23. The tube system according to claim 18 wherein the venous and arterial safety caps are arranged in one piece having an interior venous and an arterial chamber, the interior arterial chamber being connected to the interior venous chamber through a hydrophobic membrane.
 24. The tube system according to claim 18 wherein at least one of the venous and arterial patient connections has a cannula for connection to a patient, the cannula being provided in a sterile manner.
 25. A safety cap unit for a tube system comprising: an interior venous chamber for accommodating a venous patient connection; and an interior arterial chamber for accommodating an arterial patient connection of the tube system under sterile conditions, the interior venous chamber being connected to an environment by a hydrophobic membrane.
 26. The safety cap unit according to claim 25 wherein the interior arterial chamber is connected to the environment by a second hydrophobic membrane.
 27. A safety cap unit for a tube system comprising: an interior venous chamber for accommodating a venous patient connection; and an interior arterial chamber for accommodating an arterial patient connection of the tube system under sterile conditions, the interior venous chamber being connected to the interior arterial chamber by a hydrophobic membrane. 